Ocean Training 2007 Topics

ESA Satellite Missions

ESA has a established a heritage in developing successful satellite missions that enable scientific study of the oceans. Importantly, the post- ERS and Envisat era will see a succession of exciting, new science- driven Earth Explorer missions developed as part of ESA's Living Planet Programme, as well as the operational series of GMES Sentinel monitoring satellites. The first three approved Explorer missions will make specific contributions to the study of ocean circulation and dynamics, and the high latitude sea-ice covered oceans. This lecture will briefly review the objectives of the GOCE, SMOS and CryoSat-2 missions, and will indicate some of the scientific applications that shall result from their data. In addition, the presentation will indicate current plans for establishing continuity in the valuable Ku-band radar altimeter, C-band SAR, ATSR and MERIS climate monitoring datastreams, in the form of the Earthwatch GMES Sentinel-3 satellite.

MERIS Ocean Colour Principles

The MERIS session will address principles and applications of ocean colour remote sensing with special focus of the usage of MERIS data for coastal waters. The main topic is the determination of the concentrations of water constituents and optical properties from reflectance spectra of MERIS.

With its 15 spectral bands of high radiometric performance, a spatial resolution of 300 m (full resolution mode) and a revisit period of 1-3 days (latitude dependent) MERIS is in particular suited for coastal waters. However, the user of the data has to be aware of a number of problems, which are related to the variable optical properties of phytoplankton, of all kind of suspended matter and of dissolved organic compounds, all of which change the spectral reflectance. In addition these waters require a special treatment for the correction of the influence of the atmosphere.

The application ranges from water quality monitoring, determination of primary production, determination of water transparency, solar energy absorption, suspended matter transport, determination of exceptional plankton blooms etc.

Within the course all details which are necessary for a useful and critical use of MERIS data will be presented and discussed. This includes:

• Principles of ocean colour remote sensing
• Basic algorithms for open ocean and coastal waters, bio-optical models
• Basic atmospheric correction for open ocean and coastal waters
• MERIS instrument
• MERIS water algorithms for case 1 and case 2, atmospheric correction case 1 and case 2
• MERIS products overview (RR, FR, L1, L2, L3)
• MERIS flagging system
• What to find in and how to use MERIS documents: MERIS Handbook, Cyclic report, disclaimers, ATBDs, Model reference, Validation handbook
• Where are the limits of MERIS water products (e.g. concentration ranges and mixtures, atmospheric correction, sun glint)
• How to apply local algorithms
• MERIS validation procedures
• Applications - examples
• The use of BEAM software with exercises

SAR Principles

The Synthetic Aperture Radar - A(SAR) session will address principles and application of the imaging radars that achieve high resolution by using a synthetic aperture processing technique. Their view of the ocean is unhindered by clouds, and they have so called all-weather day and night capabilities. Via resonant Bragg backscattering from centimetre long waves the imaging radars measure the spatial distribution of sea surface roughness with a horizontal resolution of a few tens of meters. This fine- scale resolution gives the SAR the unique capability to observe a number of oceanic and atmospheric phenomena whose characteristic signatures appear in the patterns of sea surface roughness such as surface and internal waves, current fronts, surface wind variability, oil or natural slicks.

The first part of the session will present the basic principles of SAR imaging mechanisms. The second part will explain how to interpret radar images and provide quantitative estimates of waves, near surface wind, current features, oil spill, and sea ice.

There will be interactive practical training in which both the interpretation of oceanic signatures and the transformation of SAR images to geophysical quantities (wind, waves, current, etc.) will be demonstrated using real data from the Envisat/ERS archive.

AATSR Principles

The Advanced Along-Track Scanning Radiometer (AATSR), now flying on ENVISAT, is the third in a series of accurate infrared radiometer sensors designed to deliver sea surface temperature (SST) measurements of sufficient accuracy, better than 0.3K, combined with great stability, that they can be used as climate data records. The (A)ATSR instruments are unique in terms of their design and their ability to deliver extremely accurate SST skin observations. This short introduction will provide students with an overview of the (A)ATSR, its application and practical experience handling AATSR data.

The basic principles of remote sensing in the infra-red region of the electromagnetic spectrum will first be reviewed and used to introduce and explore the innovative design of the (A)TSR series of instruments.

We will then review the modern definitions for SST including a review of the surface skin temperature deviation, SST at depth and diurnal variability. The particular SST retrieval process used by the (A)ATSR (which retrieves an estimate of the SST skin temperature) will be presented.

Finally, the (A)ATSR data set and applications of (A)ATSR will be presented.

Practical sessions will cover the following.

• Introduction to the UNESCO Bilko image processing system and explore the various elements of this system using (A)ATSR data.
• End-to-end process of deriving SST skin from (A)ATSR Brightness temperatures will be given. If time is available, a second Bilko lesson exploring ATSR-2 monthly mean SST will be available.
• Some of the basic operations of examining global data. The data to be examined will be AATSR level 3 products, in the form of monthly means of Global SST. These can be obtained from:
  http://envisat.esa.int/level3/aatsr/

The operations to be demonstrated will be those of examining inter-seasonal variability, searching for anomalies, creation of Hovmueller diagrams (time-longitude plots) to examine the progression annual or periodic phenomena such as the Tropical East Pacific upwelling. This lecture will use the ATSR Global Analyser, an IDL tool specially developed for training purposes. As an alternative, the Bilko package can also be used for this purpose and its use will be demonstrated.

Collectively, this course will provide sufficient background information, practical instruction and tools to apply (A)ATSR SST data products in a variety of applications.

Principles of Radar Altimetry

Radar altimeters have been flown on satellites for many years and have become a firm part of the climate and ocean observing system. The RA session will address principles and applications of radar altimetry with focus on open and costal ocean applications. In addition some of the emerging new applications over ice and land will also be reviewed. As for all microwave instruments, their observing capability is unaffected by the atmosphere and therefore allows to observe dynamical features of the ocean with high along- track resolution (10 km). A RA is known for its high-precision measurements of sea surface height (the shape of the surface), but provides also important information about surface wave height and about surface wind speed.

The session will present first the basic principles of RA measurements and will discuss important interaction processes of the radar pulse with the atmosphere and geophysical phenomena that need to be known in order to obtain high accuracy data.

The session will then discuss additional information that is required to use RA data for dynamical ocean studies, such as marine geoid fields or in situ data.

Finally the session will discuss various ongoing and anticipated applications of RA.

The last part of the session will include interactive practical training using the new ESA RA tool box to train students in the interpretation of oceanic signatures of RA data (SSH, waves, wind speed) using real data from the Envisat/ERS archive.

This course will provide background information, practical instruction and tools sufficient to apply RA data products in a variety of applications.